The present invention relates to method for preparing casing for use in a wellbore.
Within the context of petroleum drilling and well completions, wells are typically constructed by drilling the well bore using one tubular string, largely comprised of drill pipe, then removing the drill pipe string and completing by installing a second tubular string, referred to as casing, which is subsequently permanently cemented in place. The installation of casing, in this typical construction requires that the casing be run into long boreholes, some having horizontal stretches. In these horizontal stretches, the casing must be installed by pushing it along the borehole. In so doing the casing is pushed in engagement with the borehole wall.
Recent advances in drilling technology have enabled wells to be drilled and completed with a single casing string, eliminating the need to xe2x80x98tripxe2x80x99 the drill pipe in and out of the hole to service the bit and make room for the casing upon completion of drilling. This change is motivated by potential cost savings arising from reduced drilling time and the expense of providing and maintaining the drill string, plus various technical advantages, such as reduced risk of well caving before installation of the casing.
Once installed either in a standard way, by running in after a wellbore is drilled or by use as the drill string and the wellbore liner, casing is often cemented in place. Cementing is often adversely affected by movement of the casing once the cement has hardened.
The use of wellbore casing, including during installation through deviated wellbores or by drilling with casing and as a wellbore liner, challenges the performance requirements of the casing.
Any advancements in the wellbore casing wherein devices are attached to the outer surface of the casing, requires the devices be attached in a rugged way to the casing, since the devices must be installed at surface and conveyed downhole with the casing. In addition, any method for attaching the devices must not compromise the integrity of the casing and the devices themselves must be inexpensive since, even if used only to facilitate installation, they must be left downhole with the casing.
A method has been invented for preparing casing for use in a wellbore. The casing produced by the method is particularly suited to overcome one or more problems encountered in running casing into a borehole, using the casing as a drill string and cementing the casing in place in the borehole. In the method, a device supporting use of the casing in a wellbore is crimped onto the outer surface of the casing. The device supporting use of the casing in a wellbore can be a device for supporting installation of the casing, either by standard run in operations or by use as a drill string, or can be a device for supporting the cementing of casing into the borehole.
The device supporting casing installation can be to facilitate run in through the borehole, to maintain casing positioning relative to the borehole and/or to accommodate wear against the wall of the borehole into which the casing is run.
The device supporting casing cementing, can be to enhance engagement between the casing and the annular cement between the casing and the borehole wall.
The devices supporting the use of casing in a wellbore are attached to the casing to create a connection having structurally significant axial and torque load transfer capacity. When using methods according to the present invention, the load transfer capacity of the connection between the device and the casing can be arranged to substantially prevent significant relative movement of the device on the casing under loads that may be encountered when installing one or more of the casing joints as a liner into a wellbore which has been drilled using a conventional drilling operation or when using one or more of the casing joints as components of a tubular string used for drilling and lining a well bore.
Thus, in accordance with one aspect of the present invention, there is provided a method for preparing a casing joint for use in a wellbore, selecting a joint of casing having an outer diameter and an outer surface and capable of receiving a device thereon by crimping and selecting a device supporting the use of the casing in a wellbore, the device having an outer facing surface, an inner bore sufficiently large to allow insertion therethrough of the joint of casing, and at least one tubular section on the body, the portion of the inner bore extending through the tubular section having an internal diameter capable of loosely fitting about the outer diameter of the joint of casing; positioning the device on the joint of casing such that the joint of casing extends through the inner bore; and crimping the device onto the joint of casing by applying an inward, substantially radially-directed force to a plurality of points about an outer circumference of the tubular section causing it to plastically deform inwardly and come into contact with the outer surface of the joint of casing, applying such additional inward, substantially radially directed force as required to force both the tubular section of the device and the outer surface of the casing to displace inwardly an amount at least great enough so that when the force is released, an interference fit is created between the device and the casing.
The step of applying substantially radially-directed force to a plurality of points about an outer circumference of the tubular section is termed herein as xe2x80x9ccrimpingxe2x80x9d.
Preferably, by selection of casing, device supporting use of the casing in a wellbore and/or force applied, the inward displacement of the casing outer surface is not so great that the drift diameter of the casing is excessively reduced. In one embodiment, the casing is not displaced inwardly beyond the drift diameter. However, in another embodiment, the inward displacement of the casing outer surface causes the inner diameter of the casing to be reduced beyond the drift diameter of the casing.
In one embodiment the method can be used to produce casing for wellbore completion, in another embodiment the method can be used to produce casing for use in a drill string and in another embodiment the method can be used to produce a casing joint particularly suited for cementing into a wellbore. The device supporting use of the casing can be selected from those useful for facilitating run in of the casing, those for controlling the positioning of the casing within the borehole, those for accommodating wear against the wall of the borehole into which the casing is run, those for use in anchoring the casing in the wellbore to inhibit relative movement between the casing string and the wellbore wall or those providing combinations of the foregoing.
Frictional forces enabled by the interference fit at the inwardly displaced section provide the mechanism by which structurally significant axial and torsional load may be transferred between the device and the casing substantially without slippage therebetween.
The casing on for use in the present invention must be capable of accepting the hoop stresses of crimping without becoming unstable, for example, without buckling or crumpling. This generally requires that the casing be thick-walled, for example, having an external diameter to thickness ratio (xe2x80x9cD/txe2x80x9d) less than 100 and preferably less than 50.
To be most generally useful for this method, the devices useful in the present invention should be amenable to rapid field installation on joints of casing having at least one non-upset end.
The tubular section of the device under application of load at a plurality of points about its circumference has an elastic resiliency less than the elastic resiliency of the casing onto which it is crimped. The tubular section can be cylindrical or largely cylindrical with some radial or axial variations to the internal diameter or outer surface. The tubular section should be substantially circumferentially continuous such that a hoop stress can be set up during the radially inward displacement at a plurality of points about the circumference of the outer surface of the section. The tubular section should be capable of accepting the hoop stresses of crimping without becoming unstable, for example, without buckling or crumpling. This generally requires that the section be thick-walled, for example, having an external diameter to thickness ratio (xe2x80x9cD/txe2x80x9d) less than 100 and preferably less than 50.
The loose fit of the section about the casing must be sufficient to accommodate the variations of the outer diameter of the casing intended to be used.
A device selected to facilitating run in of the casing can include a ramped leading edge to facilitate riding over surface contours on the borehole wall or to facilitate raising the casing such that protrusions, such as casing connections, on the casing outer surface can pass along the borehole without digging into the formation or getting hung up on shoulders in the borehole wall.
A device selected to accommodate wear against the wall of the borehole into which the casing is run can include bearing surfaces capable of withstanding extended abrasion against borehole surfaces and sufficient to withstand the rigors encountered during installation into or the drilling of at least one well. The bearing surfaces should withstand abrasion better than the material of the casing and can be, for example, hard facing, which is the treatment of steel to increase its hardness, ribs, lines of weldments, hardened inserts, etc.
A device selected from those useful for controlling the positioning of the casing within the borehole can provide for spacing the casing from the borehole wall in which it is to be used and, in particular, centralizing or stabilizing the casing within the hole. Thus, in one embodiment, the thickness of the device is selected such that once the bearing member is crimped onto the casing, the device extends radially out beyond the outer surface of the casing. In addition, the thickness of the bearing member at the bearing surfaces can be selected such that the bearing member acts as a centralizer or a stabilizer, with consideration as to the inner diameter of the borehole in which the casing is to be used.
A device selected to anchor the casing in the annular confining material, such as cement, has a plurality outwardly projecting abrupt diameter changes spaced along its length from end to end. By abrupt, is meant that the diameter changes create shoulder that preferably are substantially perpendicular to the axis of the casing or alternately may be sloped with an angle of at least 20xc2x0, and more preferably at least 45xc2x0 relative to the axis of the casing. The ability to efficiently transfer axial load between the anchoring device and the wellbore wall through the confining material such as cement typically placed in the annulus between the casing and wellbore wall will depend on the tendency of the multiple abrupt diameter changes to displace the confining material as axial movement is attempted. To provide a significant improvement in the anchoring function of a threaded and coupled anchored casing joint, the total volume swept by the multiple abrupt diameter changes preferably should be of the same order as that already swept by the face of the casing joint coupling or collar for a given amount of axial movement. This collar face area is typically approximately equal to the joint body cross-sectional so that the swept volume is this area times the axial displacement. Therefore, it is preferred that the relevant upper or lower shoulder areas of the diameter changes of the anchoring device should in total create an area equal to the cross-sectional area of the anchored casing joint body. Otherwise stated, the total axial area presented by the diameter change or shoulder to the confining material in the direction of movement should preferably be at least equal to the cross-sectional area of the anchored casing joint tubular body.
In addition, the diameter changes preferably should be of sufficient magnitude to result in significant inter-penetration with the confining material. There may be gaps between the confining material and the anchor joint tubular outer surface, such as the micro-annulus reported to occur between cement and a tubular. In addition, the radial stiffness of the confining material may allow it to deflect away from surfaces where the diameter change tends to cause loading during axial displacement of the casing string. For these reasons, it is preferred that the diameter changes be greater than 0.5% of the tubular diameter, more preferably greater than 1% of the diameter.
In one embodiment, the method provides an a casing joint, termed herein an anchor joint, comprising a joint of steel well casing having external devices for anchoring, which are steel rings, affixed by crimping in locking engagement with the tubular wall. Preferably the rings are cylindrical, have a thickness about equal to the tube wall thickness and are spaced apart at least 10 ring thicknesses.
The number of rings and the length of the anchor joint should be selected with a view to providing adequate shoulder contact with the cement or other confining material to react the axial load tending to cause movement of the casing. Selecting the number of rings, the length of anchor joint and the frequency of anchor joints in a casing string will in part be determined by field experience.
In accordance with another aspect of the invention, there is provided a method for anchoring a casing string in a wellbore comprising: inserting a plurality of anchor joints at spaced intervals into a casing string as the string is being run into the wellbore; each anchor joint comprising a joint of casing having a plurality of external steel rings crimped in locking engagement with the joint at spaced positions along the joint; and cementing the anchor joints in the wellbore.
The external rings can be crimped onto the casing in any way such as by use of a clamp, split dies forced together by a press, collet jaws forced together by an axially loaded cone or compressor or by hydroforming. In one embodiment, a hydroforming process comprises; providing a thick-walled metal tubular compatible with a casing string; positioning a crimpable ring around the tubular, the ring being formed from a ductile material, such as steel, having a yield strength less than the tubular, the ring having an internal diameter slightly greater than the external diameter of the tubular and an external profile comprising end sections and a middle section of reduced outside diameter relative to the end sections; providing a pressure forming vessel around the ring, the vessel having an internal bore slightly larger than the outside diameter of the ring, the forming vessel having internal grooves, carrying seals, spaced to straddle the reduced diameter ring middle section and to seal against the end sections to define a pressure chamber between the seals; providing a stop tube, having a length at least equal to that of the ring, within the tubular in opposed relation to the ring, the stop tube preferably having an outside diameter less than the inside diameter of the tubular by an amount at least equal to twice the elastic limit displacement of the tubular; the vessel having a passage extending through its wall to communicate with the pressure chamber, introducing pressurized liquid into the pressure chamber through the passage and causing the ring and tubular side wall to deform inwardly until the side wall contacts the stop tube and the ring is affixed to the tubular; and repeating the foregoing steps to affix a plurality of rings to the tubular to produce an anchor joint.
As a further step, the anchor joint so produced is connected into a casing string and introduced into a wellbore.
In some aspects of the present invention, differential temperature may be used to control interference between the casing and the device supporting use of the casing according to the well known methods of shrink fitting, whereby the differential temperature is obtained by heating the device, cooling the casing, or both, prior to crimping.
However, it is preferable to avoid the requirement to either heat the device or cool the casing to obtain an interference fit. In particular, preferably sufficient interference in the crimped connection is obtained substantially only by mechanical means, without requiring a significant temperature differential between the device and the casing at the time of crimping. This purpose is realized by selecting the elastic limit of the device material, in the section to be crimped, to be less than that of the casing on which the centralizer is to be installed. In this context, the elastic limit generally refers to the strain at which the materials of the parts yield. Having the material properties thus selected, it will be apparent to one skilled in the art, that when the radial displacement applied during crimping is sufficient to force the hoop strain of the metal casing to be at least equal to its elastic limit, upon release of the load causing the radial displacement, the metal casing will tend to radially xe2x80x98spring backxe2x80x99 an amount greater than the centralizer, were both parts separated. Since the parts are not separated, the difference in this amount of spring back or resiliency is manifest as interference and fulfills the desired purpose of creating interference substantially only by mechanical means.
While a purely mechanical method of obtaining interference through crimping is desirable for most applications, the present invention can use both thermal and mechanical methods for attachment of the device to the casing.
To facilitate the frictional engagement of the crimped bearing member to the thickwall casing, the inside surface of the device, at least over the section to be crimped (i.e at least a portion of the inner surface defining the inner bore through the tubular section), can be provided with a roughened surface finish. In another embodiment, a friction enhancing material such as, for example, a grit-epoxy mixture is disposed in the interfacial region of the crimped section. Similarly, various bonding materials may be disposed in the interfacial region prior to crimping to act as glues augmenting the frictional aspects of the connection once their shear strength is developed after setting.